Images returned by raster queries may be the wrong size

Description

When using the RESAMPLE command to query for a raster, Mapguide relies on RESAMPLE returning a scaled raster of the correct size.

The arguments to RESAMPLE specify the viewport that the user is currently viewing. Suppose the viewport covers the box (0,0 200,100) in mapping space and the viewer is 2000x1000 pixels. These are all arguments to RESAMPLE. Suppose we have a raster that covers the bounds (50,50 60,60) in mapping space. This is a 10x10 unit region and it corresponds to a region on the screen that is 100x100 pixels. Instead of returning a 100x100 raster, we get a 2000x1000 raster from the raster provider. It looks ok since it gets scaled by the renderer to cover the correct spot, but the overhead becomes huge if one is zoomed out and is looking at an overview of say 100 rasters.

In order to work around this MapGuide can explicitly set the size it wants the raster to be, after completing the raster FDO query and getting more information about the raster back, but before getting the actual byte stream for the raster.